In high speed presses or in those in which the paper changes direction one or more times for the purpose of making the machine more compact, guide wheels are employed to aid in changing the direction of movement of the paper. The wheels may be arranged between stages of a multiple color press and/or may be deployed where the paper leaves the last impression cylinder and passes into a paper delivery system to be transported to a paper stack. If the wheels engage the paper in wet ink areas, smearing of ink and marring of the resulting print can occur. In an effort to avoid smearing the ink, which is typically wet from previous printing steps, it has been the practice to position the guide wheels to avoid the wet ink areas. To this end the guide wheels are constructed to permit repositioning along a supporting shaft to miss any of the wet surfaces and thus avoid marking or smearing the ink on the paper. However, it is often not possible to position the guide wheels to avoid all contact with freshly inked areas of the paper. Also, even when repositioning of guide wheels would avoid contact with freshly inked areas of the paper, it maybe impractical to effect the repositioning due to the high cost of press down-time.
Many attempts have been made to avoid (to the extent possible) contact between the wheels and the paper as it moves around the wheels to change direction. Some prior solutions have included placing cloth or blotter material on the periphery of the wheels, placing relatively thick spacers along the wheels to avoid touching the ink, and constructing wheels with serrations on the outer periphery so that as little contact as possible occurs between the paper and the wheels.
A particular problem manifested by prior art guide wheels is the problem of leading edge marking. Guide wheels are typically provided with an opening or notch in the rim which supports the paper. The purpose of the opening is to receive a gripper mechanism which grips the front edge of the paper sheet as it is about to be pulled around the guide wheel. Immediately following the gripper mechanism is the leading edge of the paper-supporting rim of the guide wheel. There is an inherent tendency for this leading edge of the rim to mark the freshly inked surface of the paper. U.S. Pat. No. 3,791,644 recognizes this problem and discloses providing an inwardly tapered leading edge having a radius smaller than the remainder of the paper-supporting surface. Although this technique may eliminate marking at the leading edge per se, it instead has been found to cause marking at the point where the taper ends and the constant radius portion of the rim begins. It is believed that support for the paper is concentrated at the point where the abrupt change in curvature occurs.
An additional problem sometimes occurs during printing. As the paper is pulled around the wheels, the flexibility of the freshly inked paper permits the paper to sag between the wheels bringing the paper into engagement with the edges at the axial extremes of the rims of the wheels. Some prior art guide wheels avoid such edge marking by providing guide wheels in the form of cylinders extending the entire width of the paper. See, for example, the aforementioned patent and U.S. Pat. No. 4,402,267. Such long, cylindrical guide wheels (or "skeleton wheels") unavoidably contact parts of the freshly inked paper but employ ink-repellent materials on the paper supporting surfaces to avoid smearing the ink. U.S. Pat. No. 3,791,644 discloses coating the outer surface of the wheel with polytetrafluoroethylene (i.e., the material sold under the trademark TEFLON). U.S. Pat. No. 4,402,267 discloses use of a loosely woven fabric on the paper-supporting surface of the wheel, the fabric having been treated with a liquid repellant material such as that sold under the trademark SCOTCHGARD. The present invention takes a different approach to solving such ink smearing problems.